In a typical multiple frames imaging (MFI) system the x-ray tube generates x-ray radiation over a relatively wide solid angle. To avoid unnecessary exposure to both the patient and the medical team, collimators of x-ray absorbing materials such as lead are used to block the redundant radiation. This way only the necessary solid angle of useful radiation exits the x-ray tube to expose only the necessary elements.
Such collimators are used typically in a static mode but may assume a variety of designs and x-ray radiation geometry. Collimators can be set up manually or automatically using as input, for example, the dimensions of the organ environment that is involved in the procedure.
In multiple frames imaging, where typically a series of images are taken automatically one after the other, the situation is more dynamic than in a single exposure x-ray.
For such cases also collimators with partially-transparent to x-ray materials are used to manipulate the x-ray energy distribution as described in details below.
It is desired to change the distribution of the x-ray energy during the MFI session so that for at least 2 different frames of the MFI session the distribution of the x-ray beam will be different.
In MFI the x-ray radiation is active for a relatively long period and the treating physician typically has to stand near the patient, therefore near the x-ray radiation. As a result, it is desired to provide methods to minimize exposure to the medical team. Methods for reducing x-ray radiation intensity have been suggested where the resultant reduced signal to noise ratio (S/N) of the x-ray image is compensated by digital image enhancement. Other methods suggest a collimator limiting the solid angle of the x-ray radiation to a fraction of the image intensifier area and periodically moving the collimator to expose the entire input area of the image intensifier so that the Region of Interest (ROI) is exposed more than the rest of the area. This way, the ROI gets high enough x-ray radiation to generate a good S/N image while the rest of the image is exposed with low x-ray intensity, providing a relatively low S/N image or reduced real-time imaging, as per the collimator and method used. The ROI size and position can be determined in a plurality of methods. For example, it can be a fixed area in the center of the image or it can be centered automatically about the most active area in the image, this activity is determined by temporal image analysis of s sequence of cine images received from the video camera of the multiple frames imaging system.
It is desired to provide collimators solutions to enable reduction of dose during MFI.
It is also desired to provide a method to move the collimator elements so as to support best imaging results.
It is desired to provide a method to handle the effects of the motion on image quality.